1. Field of the Invention
The present invention relates to a control apparatus for controlling characteristics of a support unit which supports a vehicle body including a suspension and/or stabilizer in order to obtain the most advantageous characteristics using fuzzy logic with respect to the state of the traveling vehicle.
2. Description of Related Art
When a vehicle is traveling, in order to have a comfortable ride, characteristics of a support unit of a vehicle body should be adapted to be SOFT. More specifically, the damping force of a suspension should be reduced, a spring constant of the suspension should be made smaller to be softer, and the torsion quantity of the stabilizer should be lessened. On the other hand, to achieve higher operation stability, the characteristics of the support unit of the vehicle body should be made HARD. That is, the support unit should be adapted such that the damping force of the suspension is made larger, the spring constant of the suspension is heightened to be tighter, and torsion quantity of the stabilizer is made greater.
Then, there has been developed a system which switches the characteristics of the support unit to SOFT (or MEDIUM in between HARD and SOFT) when the vehicle is normally traveling and to HARD when conditions of the road surface change by driving an actuator for the support unit.
As this type of system, there are control apparatus disclosed in, for example, U.S. Pat. Nos. 4,789,935 and 4,796,911. In conventional control apparatus as described above, there have digitally been processed such subjective and vague factors as operation stability and comfort to ride in the vehicle which affect the characteristics of the support unit. In other words, those conventional control apparatus employ a method of digital decision, by which such factors as mentioned above are prioritized and processed to be binary by a predetermined threshold, and according to this processed result, the characteristics of the support unit can be judged. There, then, exists a problem in the conventional control apparatus that the characteristics of the support unit cannot be sufficiently judged so that the support unit cannot be controlled with high accuracy. And, there exists another problem in that there is no clear reference point to prioritize both of these factors.
In addition, once the characteristics of the support unit have been set to be in a HARD mode, the state of this HARD mode is adapted to be maintained for a predetermined period of time in order to prevent hunting of the actuator of the support unit. Factors to affect the characteristics of the support unit are normally transient, and once the characteristics of the support unit have been set to the HARD mode because of such transient factors, the characteristics can not be put back to be the SOFT (or MEDIUM) mode, even if the driver wishes. Thus, there exists a problem that the most advantageous control for the characteristics of the support unit cannot be performed.